Conventionally, a torque sensor for sensing steering torque generated when a driver and the like steers a steering component and an electric power steering device for calculating an amount of assist in response to steering torque sensed by the torque sensor to reduce the steering torque by the driver are well known. It is known that, when a torque sensor is applied to an electric power steering device, two torque detection sections are provided to improve safety and abnormality is detected based on the torque signals transmitted from the two torque detection sections. For example, in Japanese Patent No. 3,917,725, two steering torque detection sections which include a steering torque sensor and a steering torque detector having a torque signal detector and fault detection section are provided. In addition, a switching section is provided. When one steering torque detection section determines a self fault, the switching section switches the one steering torque detection section to the other steering torque detection section.
In Japanese Patent No. 3,917,725, a power supply line and a ground line may be required between the torque sensor and the control section in addition to a total of four lines: two signal lines from a torque signal detector; and two signal lines from fault detection section. Thus, it may be necessary to provide at least six lines. That is, in Japanese Patent No. 3,917,725, the signal lines are greater in number by the number of the signal lines from the fault detection section in comparison with the case where a total of four wires: two signal lines from a torque signal detector; a power supply line; and a ground line, are provided between a torque sensor and control section. Therefore, it may be necessary to use large-sized connectors and terminals inside the control section increase in number, which causes the overall system to be larger.